760 mg (2.64 mmol) of the compound from Example 53A and 0.55 ml (3.9 mmol) of triethylamine are dissolved in 7 ml of anhydrous N,N-dimethylformamide. 16 mg (0.13 mmol) of 4-dimethylaminopyridine and 1.09 g (3.95 mmol) of tert-butyl(chloro)diphenylsilane are added, and the mixture is stirred at RT for 2 h. The mixture is then added to water and, after phase separation, extracted three times with ethyl acetate. The combined organic phases are washed twice with water, dried over sodium sulphate, filtered, and evaporated under reduced pressure. The residue is purified by chromatography on silica gel (cyclohexane/ethyl acetate 5:1). This gives 971 mg (58% of theory) of the desired product.
